Oil Pump Rebuild

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
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Armyspecial
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Oil Pump Rebuild

Post by Armyspecial » Fri Feb 26, 2010 5:49 am

Nearing completion of my Oil pump rebuild and have a couple of questions.

How important is the thickness of the Rotor disc? I have bought a rebuild kit and the disc is slightly thinner then the original!! I would have expected it to be thicker due to wear? It seems to fit flush in the recess and does not push the Gear past the end of the pinion shaft, so is this ok?

Also, there is a measurement for the end play of the Pinion Gear in the cover housing. I cant see an easy way to take this measurement, but i assume the important thing is that the gear does not pertrude past the end of the pinion shaft or has too much of the shaft showing when seated on the Rotor Disc?

Lastly, i understand about adding Gaskets between the cover and housing to increase the end play of the driven gear on the shaft, but how important is this measurement. The TM makes reference to a 5 digit reading (0.0312) but i only have the means to measure 3 digits after the decimal point. How accurate do i need to be??

Lastly, should the gasket for the Oil Relief Spring retainer be Copper?

Thanks Guys.
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Re: Oil Pump Rebuild

Post by 41jeeps » Fri Feb 26, 2010 7:18 am

A jeep oil pump is a low pressure pump, hence the tolerances are not that critical.
However, when the tolerances are not within the limit, she can cause oil pressure problems when the engine oil becomes hot and thin.
If your rotor disk plate is not worn, pitted or damaged, the best thing you can do is reuse it.
This is a rule for every original part...if good, reuse it :!:
A smaller plate is not so good as it will influence the play from the oil pump pinion versus oil pump shaft.
The cover gasket should be kept as thin as possible.
The rule is :arrow: as little play as possible and no drag.
Do you have shim gaskets for the cover ?

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Re: Oil Pump Rebuild

Post by Armyspecial » Fri Feb 26, 2010 7:29 am

When you say "No Drag", if i push the shaft towards the pinion when assembled, there is drag but is this simulating normal use?

Yes i have a whole bunch of different thickness gaskets supplied with my engine gasket set.
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42 Ford GPW 52726 Hood No 20132506 (Actual) DOD 4TH AUG 42 (Ex NAAS Oceana)
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Re: Oil Pump Rebuild

Post by Wolfman » Fri Feb 26, 2010 7:40 am

The disc serves three purposes.
It provides a wear sureface for the pinion since the shaft assembly and pinion don't turn on the same center.
It provides clearance between the pinion and shaft assembly.
It determines how deep the pinion sets in the pump body.
To measure pinion side clearance, lay a straight edge across the open end of the pump body with the pinion laying in the body and measure the clearance. Adjust the pump body gaskets to set the clearance between the straight edge and pinion.
A feeler gauge would be the weapon of choice for this measurement.
Clearance is in the book. Don't remember off the top of my head. Not much.
If this clearance is too great without any gaskets, the disc is too thin or you have a lot of wear.
The most likely effect of too much clearance would be an oil pressure drop when the engine is hot, especially at low speeds.
When the pump is assembled, it should turn freely.
As far as taking measurments to the forth decimal point. Three should be fine.
No drag is to turn freely. You shouldn't feel any binding as the shaft is turned.
Mike Wolford
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Re: Oil Pump Rebuild

Post by Armyspecial » Fri Feb 26, 2010 8:09 am

Thanks Guys.

That should get me where i need to be.

I will check the original conponents and reuse if possible. I just assumed that renewing the internal conponents was the way to go.

Thanks again

Richard
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Re: Oil Pump Rebuild

Post by 41jeeps » Fri Feb 26, 2010 8:59 am

Mike, I do not want to change words with you, but I do not completely understand your explanation.
I just looked over a disassembled oil pump, and this is what I think is how things work :arrow: .
Please let me know where things goes wrong…
The cover has a step that sink in the pump body for centering purposes.
The shaft is deep down into the body to give clearance for the step on the cover.
With the pinion removed, and the cover installed without gasket, the shaft should freeze when the cover is pressed to the body.
The gaskets should shim the cover away from the shaft and the shaft should become free turning.
The manual gives a very small end play with the cover installed and the gaskets in place.
One can measure the tolerance by pushing the shaft down ( to the cover ) and take a measurement, and then pull the shaft up ( away from the cover ) and take a new measurement.
The differences between both measurements is the tolerance.
To do that one should first install the driven gear that a feeler gauge can be used according to the manual.
The cover should always be bolted together tight to compress the gaskets and simulate the same situation as it is installed on the engine.
The disc is as you said is a wear plate or friction plate, or bearing plate whatever one want to call it :roll: .
The thickness dictates the end play from the pinion between cover and shaft, as when installed it is sandwiched between those parts.
This end play should be kept minimal and measured with a straight edge across the top of the shaft with the disk and pinion inside.
I would aim for equal height rather than play...
Maybe the new disk is a tiny bit thinner to allow the workshop to skim the shaft top end slightly and remove the wear.
This is just a guess as I do not know if shims for the disk are available or different disk thicknesses have been made for rebuilds.
Anyway, to my opinion a smaller new disk is not the right solution, I advise to use the original disk if it has no wear or damage.
When looking at the pump, one can see that the pump body is a wear part.
The shaft has no bearings, and when it takes wear the shaft upper end start to rub against the housing.
When severe play comes between the housing and upper end of the shaft the pump will start to leak internally.
Hence, a repair kit in a worn pump housing will not give the desired results.
One should start with a check up from the housing before buying a rebuild kit.

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Re: Oil Pump Rebuild

Post by Armyspecial » Fri Feb 26, 2010 12:55 pm

Ok Guys, rebuild is now complete. I used the old parts which were all within tolorance and made the job a bit easier. Only 1 gasket needed between top and body.

The only question you didn't answer for me was the size/type of the Oil Relief Spring Retainer Gasket.

Richard
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Re: Oil Pump Rebuild

Post by 41jeeps » Fri Feb 26, 2010 2:50 pm

A copper crush washer is OK.
Not much oil pressure there.
Probably you will need to remove the retainer for adding or removing shims after a test run.
If all the shims are out and the pressure is still to high, one can install 2 copper crush washers and relieve more pressure that way.
Before installing the pump, squirt oil in it.
A well oiled pump has the tolerances filled with oil which contributes for a fast oil pick up on first start.

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Re: Oil Pump Rebuild

Post by Wolfman » Sat Feb 27, 2010 7:48 am

Glad you have your pump together Richard.
41, seems we are accomplishing the same mission only in a slightly different way.
In the end, both methods will give shaft end play and pinion side clearance measurements which will determine good pump operation.
I agree with what you say on your method.
Been doing it my way for 40 years with a success rate to back it up.
Mike Wolford
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AOPA ( 46 yrs)
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Re: Oil Pump Rebuild

Post by 41jeeps » Sat Feb 27, 2010 9:45 am

Been doing it my way for 40 years with a success rate to back it up.
I never going to catch you up Mike, I have left the trade after only 20 years due to an accident, and I have always worked at jeeps as a hobby.
And my brother has 3 mechanics in his business, and all are good, and all have different ways to accomplish things success fully :D

Best Regards.

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Re: Oil Pump Rebuild

Post by Johan WILLAERT » Thu Feb 01, 2018 12:44 am

Bringing this back to the top with a question...

Recently installed a 'rebuilt' pump to a reconditioned engine... Upon starting there was little oil pressure which further reduced within a few seconds...
Switched off of course and upon disassembly the oil pump revealed a missing rotor disc.

I suppose this was the reason for not having any or the very low pressure... But how does the rotor disc affect the pressure that much?

Just trying to understand how the pump works, thanks!

Johan
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Re: Oil Pump Rebuild

Post by Johan WILLAERT » Thu Feb 01, 2018 8:10 am

Thanks!
MVPA#14204
Huffman D50546 (1942)
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Re: Oil Pump Rebuild

Post by artificer » Thu Feb 01, 2018 11:07 am

The oil pump only produces flow.
It is resistance to that flow is what causes pressure.
Something missing in the oil pump or too large a clearance will cause internal leakage resulting in pressure loss [plus heat generation] as Johan has experienced.
Replacing the missing disc, checking clearances, reassembling & the pump should be fine.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: Oil Pump Rebuild

Post by Chuck Lutz » Thu Feb 01, 2018 11:59 am

Without splitting hairs here, this same debate has been run down multiple times...does the pump produce pressure or just flow and resistance causes pressure? Well, the answer is YES.

Any liquid being forced through a smaller area will have an INCREASE in the pressure....no argument there.

I worked as a CDF firefighter one summer...and if you rolled out a hose connected to the pump on the truck with no nozzle on it you got flow, when you put your hand over the end of it, it pushed your hand away pretty fast...because the pump created PRESSURE and FLOW! Attaching a nozzle with a smaller diameter orifice than the diameter of the hose increased the PRESSURE in which the water came out of the hose.

So you can't have pressure without flow and you can't have flow from the pump without the pump expelling it under some degree of pressure. So, the FLOW from the pump is a result of the PRESSURE created by the pump to expel it.

So let's save six pages of discussion on the topic for yet another time and agree that RESTRICING the flow of a pump can raise PRESSURE and that the FLOW from that pump is expelled under PRESSURE.
Chuck Lutz

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Re: Oil Pump Rebuild

Post by rjbeamer » Thu Feb 01, 2018 12:58 pm

Good day Chuck. You have had a discussion in the past on Pump Hydraulics on this forum. And again you are showing that you don't understand the basics. You should have studied a little more when you worked for CDF. Any good Fire Engineer will be able to straighten you out. Look at the Quote below and then click on the site that I am listing it from.


" When a hydraulic pump operates, it performs two functions. First, its mechanical action creates a vacuum at the pump inlet which allows atmospheric pressure to force liquid from the reservoir into the inlet line to the pump. Second, its mechanical action delivers this liquid to the pump outlet and forces it into the hydraulic system."

"A pump produces liquid movement or flow: IT DOES NOT GENERATE PRESSURE. It produces the flow necessary for the development of pressure which is a function of resistance to fluid flow in the system. For example, the pressure of the fluid at the pump outlet is zero for a pump not connected to a system (load). Further, for a pump delivering into a system, the pressure will rise only to the level necessary to overcome the resistance of the load"

http://www.hydraulicspneumatics.com/200 ... ulicPumpsM

Roger


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